1. Field of the Invention
This invention relates to water treatments and more particularly to water purifiers which are useful in purifying raw water from lakes or rivers in order to remove manganese and iron components and colored matters therefrom. It also relates to a method for making such water purifiers.
2. Description of the Prior Art
Recent trends toward pollution of lakes and rivers are beyond the bounds of imagination, leading to an increase in amount of raw water which is rather unsuitable for use as city water. This in turn requires complicate treating apparatus with an attendant rise of treating cost.
Several methods of removing manganese and iron components and coloring matters such as humus from raw water are known including an oxidation method using ozone or oxidizing agents, an adsorption method using active carbon, a contact filtration method using manganese-deposited zeolites, a coagulating sedimentation method using coagulants, and combinations of these methods.
The oxidation method using ozone or an oxidizing agent such as potassium permanganate is disadvantageous because of the high treating cost. Especially, use of ozone requires an additional equipment of preventing air pollution. The adsorption method using active carbon is not effective because active carbon has little adsorptivity of manganese and iron components and is low in removability of coloring matters.
The contact filtration method makes use of manganese zeolite which has manganese dioxide deposited on the surface thereof. This type of zeolite is prepared by immersing zeolite in a solution containing divalent manganese ions and adding an oxidizing agent such as, for example, potassium permanganate to have manganese dioxide deposited on the surface of zeolite. In this method, however, a large amount of an expensive chemical such as potassium permanganate is used, leading to a high treating cost. If raw water being treated has a high content of manganese, it cannot be removed efficiently. Because manganese dioxide is deposited on the surface of zeolite, the dioxide may readily fall off and be lost with the deposited zeolite deteriorating in quality.
It is generally accepted that manganese dioxide itself has the effect of removing manganese, iron and coloring matters from water. For use as a water purifier, manganese dioxide has to be reduced into pieces having a suitable range of size. For instance, chips of electrolytic manganese dioxide removed from the electrode or natural manganese dioxide may be crushed to have a desired particle size. Alternatively, manganese dioxide powder may be bonded with use of an inorganic binder such as alumina cement and shaped to have a suitable particle size. However, the former manganese dioxide particles are disadvantageous in that a reactive area is relatively small. On the other hand, the particles obtained by using inorganic binder have the drawback that active surfaces of the manganese dioxide are covered with the inorganic binder added and the purification effect is lower than the one achieved by the starting manganese dioxide material itself.